The present invention relates to a control device for controlling a hydraulically movable tool carried by a machine, and more specifically, to a control device having a light detector and a gravity-based sensor which controls a lift mechanism of a machine to maintain a selected horizontal orientation and elevation of a tool carried by the machine.
A Grade Control Receiver is a dedicated laser receiver that includes internal valve drivers capable of controlling PT, PWM, and Danfoss(copyright) hydraulic valves. Grade Control Receivers are commonly used in construction and agriculture applications for controlling the horizontal orientation (slope and pitch) and elevation of a wide-range of industrial tools, such as trowels, blades, 3-point hitches, and screeds. For these applications, the prior art practice has been to use at least a pair of laser receivers in order to determine the orientation and elevation of hydraulically controlled ends of a tool carried by a machine. For example, U.S. Pat. No. 5,951,612 to Sahm discloses using a pair of laser receivers to determine the slope, pitch, and elevation of an implement on an earthmoving machine. U.S. Pat. No. 4,807,131 to Clegg discloses a system using two laser receivers mounted at the opposite ends of an earthmoving blade, wherein the control system measures the side to side slope of the blade by determining the difference in elevation of the two laser receivers.
While the above-mentioned arrangements provide effective ways to control the movement of a tool carried by a machine, the drawback of these prior art arrangements is the significant cost associated with using a plurality of laser receivers. This is particularly true with fairly inexpensive tool attachments, such as for a skid steer loader, in which the tool attachment may only be half as expensive as the pair of laser receivers. In most of the construction and agricultural applications for which these tool attachments are used typically only either the pitch or the slope is controlled, while the elevation is maintained in reference to an external light reference, such as a laser transmitter.
Therefore, there is a need for providing an economical control system which controls a hydraulically movable tool carried by a machine to maintain a selected horizontal orientation and elevation.
This need is met by an apparatus and method according to the present invention that automatically controls a hydraulically movable tool carried by a machine in order to maintain a selected horizontal orientation and elevation. The control device of the present invention comprises an integral light detector, an integral gravity-based sensor, and a computer. The control device is mounted at a known location along a longitudinal axis of the tool. The computer of the control device receives an elevation signal from the light detector indicating the relationship of the control device at the known position to an external light reference. Additionally, the computer receives an angle of deflection signal from the gravity-based sensor, which indicates either the pitch or the side-to-side slope of the control device at the known location from true horizontal. With the distances between the control device and all points along the longitudinal axis of the tool being known to the computer, the computer calculates the elevation and horizontal orientation (pitch or slope) of all points along the longitudinal axis of the tool. Once these points are calculated, the control device automatically controls each hydraulic cylinder of the machine to maintain a selected horizontal orientation and elevation of the tool.
In one aspect, the present invention is an apparatus for automatically controlling a hydraulically movable tool carried by a machine in order to maintain a selected horizontal orientation and elevation relative to an external light reference. The apparatus comprises a housing, a light detector accommodated within the housing and capable of producing a signal in response to detecting the external light reference, and a gravity-based sensor. The gravity-based sensor is also accommodated within the housing and is capable of producing a signal indicative of a detected angle of deflection of the tool from true horizontal. The apparatus further comprises a computer accommodated within the housing and electrically coupled to the light detector and the gravity-based sensor. The computer is adapted to receive the signals from both the light detector and the gravity-based sensor and to control both the selected horizontal orientation and the elevation of the hydraulically movable tool based on the signals.
In another aspect, the present invention is a method for automatically controlling a hydraulically movable tool carried by a machine to maintain a selected horizontal orientation and a selected elevation relative to an external light reference. The method includes the steps of providing a control device at a known location along a longitudinal axis of the tool, and entering into the control device a desired horizontal orientation. Both an external signal from the external light reference, indicating actual height of the tool at the known location, and angle of deflection to true horizontal are sensed by the control device. The control device determines if the angle of deflection and the external signal match the desire horizontal orientation and the selected elevation, and then responsively controls the hydraulically movable tool carried by the machine to maintain the horizontal orientation and the selected elevation.
In another aspect, the present invention is a machine for operating with an external light reference, comprising a tool, a mast attached to the tool, and a control device having a housing. The housing of the control device accommodates a computer, a light detector, and a gravity-based sensor, and is attached to the mast. The computer is operably coupled to the light detector and the gravity-based sensor, and is configured to determine both an elevation of the tool relative to the external light reference, and a horizontal orientation of the tool relative to true horizontal based on signals received from the light detector and the gravity-based sensor.
Other objects, features and advantages will appear more fully in the course of the following discussion.